Microminiaturization plays an increasingly imperative role in our daily life, especially for applications such as positioning, navigation and attitude control. Therefore, there is a need to develop highly integrated, sensitive and miniaturized gyroscopes to be incorporated as rotation sensors for the above mentioned applications.
Among all kinds of approaches in the prior art, FOG's based on Sagnac effect (R. A. Bergh, H. C. Lefevre, H. J. Shaw, “An Overview of Fiber-Optic Gyroscopes”, J. Lightwave Technol., vol. 2, n. 2, pp. 91-107, February 1984 and M. N. Armenise, C. Ciminelli, F. De Leonardis, R. Diana, F. Peluso, V. M. N. Passaro, “Micro Gyroscope Technologies for Space Applications”, Internal Report, ESA-ESTEC Iolg Project, Contract DEE-MI, May 2003) are extensively used. One of the key components inside a FOG is the photonic chip mastering optical signal processing (M. N. Armenise, V. M. N. Passaro, F. De Leonardis, M. Armenise, “Modeling and Design of a Novel Miniaturized Integrated Optical Sensor for Gyroscope Applications”, J. Lightwave Technology, vol. 19, n. 10, pp. 1476-1494, 2001. 1).
Prior to the present invention, the traditional fiber sensors such as FOG's employing LiNbO3 as the waveguide material for MIOC had been reported (U.S. Pat. No. 5,223,911). The LiNbO3-based fabrication processes result in a relatively larger and more expensive chip due to smooth waveguide bending requirement, and is not compatible with the mainstream integrated circuit processes.
Other than LiNbO3 MIOC, silicon-based MIOC had also been reported previously (U.S. Pat. No. 5,154,917, and patent application Ser. No. 11/497,020). Comparing to other types of integrated optic waveguides, cost of a silicon-based optical waveguide is relatively low because there is plenty of supply for silicon. Also, within the large operating temperature range, silicon chemical property is benign and stable. No chemical reaction is anticipated. Besides, silicon-based optical waveguides allow large angle splitting and even a 90 degree waveguide bend which greatly reduce the optic chip length from centimeter to millimeter scale, and hence cut down the optic chip cost and sensor dimension. Above all, the silicon waveguide is compatible with CMOS fabrication process, so integration of optical waveguide with electronic circuit in one optic chip is feasible.
However, so far there is no commercially available FOG's claimed on silicon-based MIOC technology due to design deficiencies or process complications. Examples such as for single mode, single polarization operations for sensor applications, U.S. Pat. No. 5,154,917 didn't address the polarizer issue, and Ser. No. 11/497,020 employed a standalone polarizer which inherently increasing the chip length and its associated optical loss.
According to the present invention, applicants have departed from the conventional wisdom, and had conceived and implemented a practical silicon-based MIOC to integrate functions of Y-junction splitter, polarizer, and phase modulators on the single optical chip through the implementation of a unique polarization diversity coupler which is capable of separating TE and TM modes in less than 100 μm length, and the two-step taper waveguide designs for single-mode, and low loss sensor applications such as for miniaturized FOG's. Such integration has additional advantages in reducing the cost of individual component package and perhaps, the effort of alignment. Moreover, through mature IC fabrication technology, the production cost could decrease and the device performance improves. The invention is briefly described as follows.